8 Jan
2014
8 Jan
'14
1:17 p.m.
This is a multi-part message in MIME format. ------=_NextPartTM-000-dc553fe8-e084-4205-a5f2-e4e48c40f662 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable > Hi,=0A= > =0A= >I'd like to ask around if someone does run oVirt=0A= > with NFS backed Storage provided by simple servers (no SAN or NAS)=0A= > and what your experience is so far?=0A= =0A= We are running OVirt (still in test phase) on three self build equal Ubuntu= =0A= NFS servers over Infiniband (50 Euros for a ConnectX card + 50 Euros a cabl= e +=0A= 400 Euros a switch). Due to massive bandwidth the bottleneck are the SATA = =0A= disks and the RAID controller. I fixed some info at http://www.ovirt.org/In= finiband=0A= Our soon to be replaced ESX infrastucture uses the same platform.=0A= =0A= > In particular I'm interested what happens if there is a connection=0A= > loss to the NFS-Volume.=0A= =0A= You can be sure that the applications in your VMs will get stuck. They usua= lly flush =0A= their write caches in regular intervals. This is directly translated into a= NFS write=0A= on the hypervisor. At least it should be configured that way otherwise you = could=0A= loose data in case of a crash. E.g. VM thinks data is persisent, but it was= only cached=0A= in the hypervisor RAM.=0A= =0A= > How does this affect running vms and the compute nodes they run on?=0A= =0A= The hypervisor has no problems at all (except you run a df command) and the= =0A= VMs usually will continue their operation after NFS recovers. Nevertheless = =0A= the are lot of timeout settings in the architecute stack that may stop a ru= nning=0A= application inside the VM. Expect do have a lot of manual cleanup after a= =0A= NFS failure.=0A= =0A= > I suspect they would first write their changes to RAM instead of virtual = HDD.=0A= > But once the RAM is full, does just the vm become unresponsive or=0A= > does the whole compute node die?=0A= =0A= That would be bad practice. See above.=0A= =0A= > I couldn't test this yet myself, but my limited experience with=0A= > NFS-Servers tells me, that they become unresponsive if they are under=0A= > heavy load and I'd like to know how this affects the vms and=0A= > computenode.=0A= =0A= Defining heavy load is basically some kind of I/O calculation. A simple=0A= example from our setup.=0A= =0A= - Each NFS server has a RAID6 consisting of 14 SATA disks (7.2K)=0A= - The top-loaded NFS server runs a minimum of 140 8K I/Os per second=0A= - Assuming a random pattern we speak of 140 Read-Modify-Write cycles=0A= - That translates to roughly to 6*140=3D840 I/Os per second.=0A= - The 14 SATA disks offer a maximum of 14*90=3D1260 I/Os per second=0A= - No wonder that the NFS server gives usually a 20% wait I/O usage.=0A= =0A= > Thanks!=0A= =0A= > PS: Bonus question: Does someone utilize the NFS-Servers also as=0A= > computenodes ?=0A= =0A= We spearated that stricly. Otherwise we would go with a Gluster FS.=0A= =0A= Markus=0A= =0A= P.S. We leave VMWare because live storage migration of OVirt VMs =0A= gives us the possibility to reduce the complexity on the storage side.=0A= ------=_NextPartTM-000-dc553fe8-e084-4205-a5f2-e4e48c40f662 Content-Type: text/plain; name="InterScan_Disclaimer.txt" Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename="InterScan_Disclaimer.txt" **************************************************************************** Diese E-Mail enthält vertrauliche und/oder rechtlich geschützte Informationen. Wenn Sie nicht der richtige Adressat sind oder diese E-Mail irrtümlich erhalten haben, informieren Sie bitte sofort den Absender und vernichten Sie diese Mail. Das unerlaubte Kopieren sowie die unbefugte Weitergabe dieser Mail ist nicht gestattet. Über das Internet versandte E-Mails können unter fremden Namen erstellt oder manipuliert werden. 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